A drive circuit for a switching element turns on and off the switching element by controlling a voltage applied to a control terminal of the switching element. In this case, a main factor determining an on-off time of the switching element is a charging and discharging time depending on a parasitic capacitance.
The charging and discharging time of the parasitic capacitance depends on a current value that flows from the drive circuit to the control terminal of the switching element. Thus, it is preferable that the current value flowing to the control terminal is increased so as to shorten the charging and discharging time. This kind of technique is described, for example, in the patent document 1. The patent document 1 discloses a configuration that forcibly brings the voltage applied to the switching element close to a power supply voltage.
In other words, the conventional drive circuit speeds up a switching operation by increasing the current value that flows from the control terminal of the switching element to the parasitic capacitance. However, in this case, it is required to increase a current supply capacity of the drive circuit. In order to solve this problem, in the patent document 2, an inductor is disposed around a current path that carries a main current of the switching element, and an induction voltage generated at the inductor is superimposed on the voltage applied to the control terminal of the switching element. The patent document 2 suggests that the above-described operation enables a high-speed operation of the switching element without increasing the current supply capacity of the drive circuit.
How to arrange an inductor with respect to a main current path becomes a problem in order to utilize the technique described in the patent document 2. In the technique described in the patent document 2, a ring-shaped ferrite core and a coil wound around the ring-shaped core are used. However, because the core is formed into the ring-shape, it is difficult to fix the core. In addition, because the core is disposed around the main current path,. a large arrangement space is required.